The present invention relates to mechanical and electronic anhydrous ammonia fertilizer application systems.
The typical electronically controlled ammonia application systems consist of a nurse tank trailed behind a tool bar which is attached to a tractor. A computer console is mounted accessible to the tractor operator.
The nurse tank is a pressure vessel which contains the ammonia in its liquid state. The liquid withdrawal valve is mounted at the top of the tank and has a dip tube which extends to the bottom of the tank. A suitable hose connects this valve to a filter connected to a main shutoff valve mounted on the tool bar. The ammonia then flows through a heat exchanger unit, then through a turbine or venturi meter, then to an electronically controlled throttling valve, then to one or more manifolds, and finally through suitable hoses to the applicator knives which insert the ammonia into the soil. In operation, it is a virtually open system from the throttling valve all the way to the knives.
The typical mechanical systems are about the same as the electronic systems, however they utilize a single manually adjustable mechanical meter which feeds the ammonia to one or more manifolds. The manifolds route the ammonia to several hoses, each of which feed a single knife. In operation, it is also an open system past the meter all the way to the knives.
As the liquid ammonia enters the dip tube located at the bottom of the tank, its thermodynamic conditions begin to change. The ammonia begins to expand. This results in the formation of ammonia vapor within the system. The swath width of the tool bar and the desired amount of ammonia per acre are entered into the computer. The computer receives signals from either a turbine or venturi type meter and from the ground speed sensor. The computer processes the data and compensates for any variations by electronically controlling the throttling valve.
These systems work fairly well, but under certain conditions problems can arise. They lose all control of the ammonia as soon as it crosses the throttling valve, in the electronic systems, or the meter, in the mechanical systems. In cooler weather the pressure difference across the system is reduced and sagging hoses can cause the formation of plugs of liquid ammonia which result in uneven distribution to the applicator knives. Crops such as corn require more than twice the amount of ammonia per acre than the smaller grain crops. The greater expansion of the ammonia across the total system often forms more vapor than a typical heat exchanger unit can handle.
It would be a distinct advantage to have an ammonia control device which would provide the means necessary to provide for greater control and application accuracy. The present invention provides such a unit.